1. Field of the Invention
The present invention relates to an image receiving sheet used for recording an image formed by electrophotography, and, particularly, to an electrophotographic OHP image receiving sheet capable of restraining a projected image from being grayed when a color image is projected using an OHP.
2. Description of the Related Art
In recent years, a method of forming a full color image by mixing either three toners having different colors, specifically, yellow, magenta and cyan or four toners having different colors, specifically, black in addition to the above three colors by using electrophotography has been put to practical use.
An image receiving sheet used in this electrophotography generally adopts a structure in which a receptor layer is formed on a substrate to record and maintain record information such as characters and images exactly. This image receiving sheet is used for OHPs (overhead projector) as communicating means used in lectures, schools, industries, and other explanatory meetings and exhibitions.
When a color image formed by electrophotography is projected by an OHP, such a phenomenon that the projected image is grayed (exhibits a gray tone) and the range of the reproduction of a tone is narrowed is observed. This is because a toner stuck to the smooth image receiving surface of an image receiving sheet is insufficiently embedded so that the surface is not smoothed and the toner is swollen granularly and incident light is thereby scattered during the projection of an OHP whereby a shadow is formed on a screen.
As a method used to solve the grayness problem, there is disclosed a method measuring and defining the molten toner inclination angle of the receptor surface of an image receiving sheet with a toner at a fixing temperature of the toner, which is described in, for example, JP-A No. 5-88400 or JP-A No. 5-197184. In a method of measuring the molten toner inclination angle, unlike the fixing condition in an actual recording printer, a toner disk is formed as a sample and an image receiving sheet and the disk are placed on a hot plate to measure the molten toner inclination angle by using an appointed measuring meter. In this method, specific instruments such as a molding member and a hot plate are required and it is necessary to take care for the aforementioned measurement. This method is not practically convenient because of, for example, dispersion of measured values.
Accordingly, it is an object of the present invention to find an electrophotographic OHP image receiving sheet which has high tone reproducibility, enables a vivid image and produces no graying phenomenon in a projected image of OHPs by a simple measuring method, thereby solving the aforementioned problem.
According to a first aspect of the present invention, there is provided an image receiving sheet printable by electrophotography and applicable to an overhead projector (OHP), the image receiving sheet being capable of forming a yellow image providing a parallel-ray transmittance of 50 % or more when the transmittance density is in a range from 0 to 1.0 by electrophotography.
The image receiving sheet is preferably capable of forming a yellow image providing a parallel-ray transmittance of 55 % or more when the transmittance density is in a range from 0 to 0.6 by electrophotography.
In the first aspect of the present invention, there is also provided an image receiving sheet printable by electrophotography and applicable to an overhead projector (OHP), wherein the following expression 1 is established between the transmittance density and the parallel-ray transmittance when the transmittance density is in a range from 0 to 0.6;
Expression 1
Yxe2x89xa7{34/(X+1.2)}+57
where X represents the transmittance density and Y represents the parallel-ray transmittance, provided that 0xe2x89xa6Xxe2x89xa60.6.
In one embodiment of these OHP image receiving sheets, a receptor layer printable by electrophotography is formed on at least one side of a substrate film.
In the first aspect of the present invention, there is also provided an image forming process capable of projecting an image by an OHP using any one of the aforementioned image receiving sheets.
Specifically, the process of forming an OHP image according to the first aspect has the characteristics that any one of the aforementioned image receiving sheets is provided, and an image is printed on the image receiving sheet by electrophotography.
According to the above first aspect of the present invention, the image receiving sheet is simply evaluated on the basis of the parallel-ray transmittance (JIS K 7105) and transmittance density (Macbeth TR-924, filter: status A blue (ISO 5-3)) of a sheet on which an image is formed, thereby obtaining an image receiving sheet which has high tone reproducibility, enables a high vivid image and produces no graying phenomenon in an projected image of an OHP with no complicated method.
According to a second aspect of the present invention, there is provided an image receiving sheet printable by electrophotography and applicable to an overhead projector (OHP), the image receiving sheet being capable of forming a yellow image providing a haze value of 40 % or less when the transmittance density is in a range from 0 to 1.0 by electrophotography.
The image receiving sheet is preferably capable of forming a yellow image providing a haze value of 30 % or less when the transmittance density is in a range from 0 to 0.6 by electrophotography.
In the second aspect of the present invention, there is also provided an image receiving sheet printable by electrophotography and applicable to an overhead projector (OHP), wherein the following expression 3 is established between the transmittance density and the haze value when the transmittance density is in a range from 0 to 0.6;
Expression 3
Zxe2x89xa632xe2x88x9217/(7X+0.6)
where X represents the transmittance density and Z represents the haze value, provided that 0xe2x89xa6X xe2x89xa60.6.
In one embodiment of these OHP image receiving sheets, a receptor layer printable by electrophotography is formed on at least one side of a substrate film.
In the second aspect of the present invention, there is also provided an image forming process capable of projecting an image by an OHP using any one of the aforementioned image receiving sheets. Specifically, the process of forming an OHP image according to the second aspect has the characteristics that any one of the aforementioned image receiving sheets is provided, and an image is printed on the image receiving sheet by electrophotography.
According to the above second aspect of the present invention, the image receiving sheet is simply evaluated on the basis of the haze value (using a haze meter manufactured by Nippon Denshoku Kogyo according to JIS K 7105) and transmittance density (Macbeth TR-924, filter: status A blue (ISO 5-3)) of a sheet on which an image is formed, thereby obtaining an image receiving sheet which has high tone reproducibility, enables a high vivid image and produces no graying phenomenon in an projected image of an OHP with no complicated method.